The invention relates to a method of determining the extent of a keratotomy incision by determining a point of increased resistance against blade advancement of an RK knife as it makes the incision. The incision is stopped when a critical level of resistance is detected. The resulting incision length optimally corrects the patients vision.
Ophthalmologists usually use "optical zone markers" to determine the length of a keratotomy incision. A radial RK incision typically begins approximately a millimeter from the outer edge of the cornea. The blade of an RK knife is moved radially inward toward an "optical zone marker" (which is a shallow indentation previously made in the epithelium by the surgeon around a central area of the cornea by pressing a stainless steel device known as a zone marker against the central cornea). An astigmatic keratotomy (AK) is performed by making the incision(s) tangential to the steepest radial curvature of the cornea in a linear or curvilinear fashion at a predetermined optical zone. The size of the optical zone markers usually is made according to nomograms or empirical formulas based on age, sex, degree of correction needed, thickness, curvature, and/or diameter of the cornea. However, such nomograms and empirical formulas are based on averages for a large number of patients, and are not necessarily accurate for a particular patient if his or her eye has "non-average" material properties.
There is an unmet need for a technique and device for optimizing lengths of keratotomy incisions based primarily on the material properties of the cornea and its behavior in response to such incisions.